Mr Cairns said Mr Bell once "wanted the press office dismissed" for the Department for Enterprise, Trade and Investment (Deti), feeling it was "not delivering enough press coverage", and he was "angry at being told he could not employ a private PR firm".

Mr Bell was also "angry" that his invite for BBC Sports Personality of the Year had been sent to Arlene Foster "in error".

Mr Cairns also told how on one occasion passing Westminster, Mr Bell told "how he would be an MP by 2020".

The former special adviser said there was a high-profile meeting with Ryanair in 2015 which was "memorable" as it had been "embarrassingly handled by Mr Bell" and a departmental official "often discussed this meeting when speaking about Mr Bell's lack of competence".

In another incident, Mr Cairns claimed Mr Bell once missed important assembly business because he overslept and had to be wakened by repeated phone calls.

The minister arrived in Stormont "with wet hair and looking like he had dressed in haste", he claimed.

But he said Mr Bell later turned on him and an official, pointing and shouting: "You two boys have f***ed up."

Mr Cairns also said that after becoming first minister, Arlene Foster expressed concern at the number of foreign trips Mr Bell was taking and ordered that he "would not engage any further foreign trips".

But the former aide said Mr Bell ignored the order and "organised foreign travel as he saw fit".

Mr Cairns said Mr Bell was once asked to meet Mrs Foster in Stormont Castle but refused, and instead spent the evening with Peter Robinson.